1. Field of the Invention
The invention relates generally to photography, and particularly to apparatus for advancing a film leader from a film cassette in a camera.
2. Description of the Prior Art
Generally speaking, commercially available 35 mm film cassettes comprise a hollow cylindrical shell having an integral throat or lipped portion which extends tangentially from the shell. A film spool on which the filmstrip is wound is freely rotatable within the cylindrical shell. The filmstrip has a leading end section, commonly referred to as a "film leader", which extends through a light-trapped slit in the throat portion to the outside of the shell. Typically, the film leader is 2-3 inches in length and is normally curled about the shell.
When loading a conventional camera with such a film cassette, a rear door of the camera is widely opened. Then, the cassette with the film leader held uncurled from around the cylindrical shell is inserted into a rear loading chamber in the camera. The manually straightened leader is positioned with its leading tip adjacent a take-up drum in the camera and with one or more of its perforations in engagement with a corresponding number of teeth of a metering sprocket located between the take-up drum and the loading chamber. This film loading operation is rather troublesome and requires a certain amount of skill and manual dexterity. Accordingly, it is rather difficult for certain people.
More recently, several bottom loading cameras have been proposed which include simple means for automatically uncurling the film leader from around the cylindrical shell as the film cassette is inserted endwise, i.e. axially, through a bottom opening to the loading chamber in the camera. For example, in commonly assigned U.S. Pat. No. 4,332,453, granted June 1, 1982, the automatic uncurling means comprises a quarter-round corner located adjacent the loading chamber in the camera and an inclined straight edge extending generally along the bottom of the camera. When a bottom door of the camera is widely opened and the cassette is initially inserted into the loading chamber, a full width (uncut) section of the film leader adjacent the throat portion of the cassette is pushed against the quarter-round corner. The quarter-round corner, in turn, deflects the full width section of the leader to position a reduced width (cut) section of the leader forward of the full width section crosswise against the inclined straight edge. Then, with continued insertion of the cassette into the loading chamber, the reduced width section of the leader is progressively straightened by its movement against the inclined straight edge. Thus, the film leader is progressive uncurled as the cassette is inserted axially into the loading chamber.
Although known recent cameras which include automatic uncurling means for the film leader appear to work satisfactorily, the structure in the camera comprising such means may tend to increase manufacturing costs to a significant extent. Moreover, as in the case of other cameras, it is possible for the film leader to become snagged during the film loading operation.
A 35 mm film cassette has been proposed which, unlike conventional film cassettes, includes a film leader that does not extend outside the cassette shell. The leader, instead, is located entirely within the cassette shell. Specifically, in U.S. Pat. No. 4,423,943, granted Jan. 3, 1984, there is disclosed a film cassette wherein the outermost convolution of the film roll wound on the film spool is radially constrained by respective circumferential lips of two axially spaced flanges of the spool to prevent the outermost convolution from contacting an inner wall of the cassette shell. The trailing end of the filmstrip is secured to the film spool, and the leading end of the filmstrip is reduced in width to allow it to protrude from between the circumferential lips and rest against the shell wall. During unwinding rotation of the film spool, the leading end of the filmstrip is advanced to and through a film passageway opening in order to exit the cassette shell. The opening has a width which is slightly less than the width of the filmstrip, thus resulting in the filmstrip being transversely bowed as it is uncoiled from the film spool, and thereby facilitating movement of the film edges under the circumferential lips of the respective flanges.
While the film cassette disclosed in U.S. Pat. No. 4,423,943 includes a non-protruding film leader which is automatically advanced to the outside of the cassette shell when the film spool is rotated in the unwinding direction, the film cassette appears to be intended to be loaded in a camera only after the film leader is advanced to protrude from the cassette shell. In the patent, it is suggested that one manually rotate the film spool relative to the cassette shell until the leader can be manually grasped and attached to a film advancing device in a camera. Thus, the loading problems regarding manipulation and snagging of the leader similarly apply to this prior art example.